1. Field of the Invention
The present invention relates to a discharge lamp lighting device. More specifically, the present invention relates to a lighting device for high-voltage discharge lamps such as metal halide lamps and the like.
2. Description of Related Art
In general, high-voltage discharge lamps such as metal halide lamps do not generate light immediately after being lit because the vapor pressure of light emitting metals does not increase immediately.
Thus, to speed up the generation of light, Japanese Patent Laid-Open Publication No. Hei-5-144577 discloses a method for applying a start-up electric power to a discharge lamp which is greater than the prescribed electric power of the discharge lamp.
However, with such conventional technology described above, because the voltage applied to the lamp is controlled to be bigger when the lamp voltage is low, then the amount of lamp current becomes excessive and thus, the electrodes of the discharge lamp are consumed easily and the lifetime of the discharge lamp becomes shorter.
For this purpose, one plausible way of curbing electrode consumption might be to control the lamp current during start-up to equal the electric current during stable lighting. However, with this method, the arc discharge becomes unstable between electrodes during start-up, the inconvenience of the discharge lamp flickering out is likely to happen and such problems as the slowing down of the generation of the light output occur.